Field of the Invention
The present invention relates to the production of nitrogen and oxygen by air distillation. It concerns, first, a process for the simultaneous production, on the one hand, of pure nitrogen under an elevated pressure of nitrogen which is higher than about 25 bars absolute, and on the other hand, of oxygen, by air distillation in a double distillation column comprising a mean pressure column and a low pressure column of the "minaret" type which produces pure nitrogen in the top portion thereof.
A specific application of the invention is the simultaneous production on the one hand of high purity nitrogen, containing less than 10 ppm oxygen, in large quantity (i.e. representing at least 20% and typically more than 30% of the flow of air being treated), at 50 to 60 bars, intended for a unit for the production of ammonia, and, on the other hand, of oxygen of an average to high purity, that is 95 to 99.5% in moles, at a pressure of about 65 bars and with an elevated yield of extraction, for the production of hydrogen by reaction of oxygen with heavy hydrocarbons, the hydrogen being intended to supply the same unit for the production of ammonia.
The term "low pressure column of the minaret type" means a low pressure column, which is part of a double column for air distillation, in which the upper end portion is supplied at the top with "upper poor liquid" (substantially pure nitrogen) which is withdrawn at the top of the mean pressure column and is thereafter expanded, and which produces, at the top, pure nitrogen under low pressure.
The pressures referred to herein are absolute pressures. Moreover, the term "low pressure" and "mean pressure" mean operating pressures of the low pressure column and of the mean pressure column of the double column, respectively.
The invention aims at providing a process enabling the production, in addition to oxygen, of nitrogen under elevated pressure, in large amounts, i.e. representing at least 20% of the flow of air being treated, with a reduced investment.